<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .mask {
            position: fixed;
            left: 0px;
            right: 0px;
            top: 0px;
            bottom: 0px;
            background-color: rgba(0,0,0,0.2);
            /* display: ; */
        }
    </style>
</head>
<body>
    <div class="mask"></div>
    <button onclick="handleClick()">点击我</button>

    <script>
        function handleClick() {
            console.log("我是按钮！");
        }
    </script>
</body>
</html>